Process for the co-production of aromatic carboxylates and alkyl iodides

ABSTRACT

Disclosed is a process for the co-production of aromatic carboxylates and alkyl iodides by the carbonylation of aromatic iodides in the presence of an alkanol and a ruthenium catalyst.

DESCRIPTION

This invention relates to a novel carbonylation process for thepreparation of both aromatic carboxylic acids or esters and an iodinecontaining compound from which the iodine values can be economicallyrecovered. The carbonylation is conducted in the presence of an alkanoland a catalytic amount of ruthenium.

The carbonylation of aromatic halides in the presence of various GroupVIII metal catalysts to obtain aromatic carboxylic acids and esters iswell known in the art. For example, U.S. Pat. No. 3,988,358 disclosesthe palladium-catalyzed carbonylation of aromatic halides in thepresence of an alcohol and a tertiary amine to produce the correspondingcarboxylic acid ester. Nakayama and Mizoroki (Bull. Chem. Soc. Japan 42,1124 (1969)) disclose the nickel-catalyzed carbonylation of aromatichalides in the presence of an alcohol and potassium acetate to producethe corresponding acid ester.

While it is known that aromatic iodides can be carbonylated the use ofthese materials has been discouraged by the cost associated with thedifficulty of recovery the iodine values. For example, the use of basicmaterials in the carbonylation of aromatic halides, such as tri n-butylamine in U.S. Pat. No. 3,988,358, results in the formation of halidesalts from which the halide values can be reclaimed only throughuneconomical procedures involving severe chemical treatments.

We have discovered a process which not only results in the carbonylationof aromatic iodides to aromatic carboxylic acids or esters in excellentyields and at excellent rates of conversion but also a process whichresults in production of alkyl iodides from which the iodine values canbe economically recovered. In this invention the carbonylation isconducted in the presence of an alkanol and a catalytic amount of aruthenium catalyst under aromatic carboxylic ester and alkyliodide-forming conditions of temperature and pressure. The advantageafforded by our invention over the prior art is two-fold. First, theruthenium-based catalyst has not been disclosed or recognized in theprior art to be an efficient carbonylation catalyst for aryl halides.Second, the iodine values in the alkyl iodide may be readily recoveredby simply flashing the relatively volatile alkyl iodide from the mixtureresulting from the carbonylation reaction. This can be accomplishedeither in the carbonylation reactor or, more preferably, in a pressurereduction vessel to which the mixture resulting from the carbonylationreaction is fed.

The ratio of aromatic acids to esters produced in the present inventionis dependent on the ratio of alkanol to water present in thecarbonylation reactor and on the choice or organic co-solvent. Ingeneral, minimizing the ratio of alkanol to water maximizes theproduction of acid. Conversely maximizing the ratio of alkanol to watermaximizes the production of ester.

The aromatic iodides which may be used in our process may be monoiodo orpolyiodo, e.g. di-, tri-and tetra-iodo aromatic compounds. The aromaticnucleus or moiety can contain from 6 to 18 carbon atoms, preferably 6 to10 carbon atoms and may be carbocyclic aromatic such as benzene,biphenyl, terphenyl, napthhalene, anthracene, etc., or heterocyclicaromatic such as pyridine, thiophene, pyrrole, indole, etc. In additionto one or more idodine atoms, the aromatic moiety may be substituted byvarious substituents inert under the conditions employed in our process.Examples of such substituents include alkyl of up to about 12 carbonatoms such as methyl, ethyl, isobutyl, hexyl, 2-ethylhexyl, nonyl,decyl, dodecyl, etc.; cycloalkyl of about 5 to 12 carbon atoms such ascyclopentyl, cyclohexyl, 4-butylcyclohexyl, etc.; hydroxy; alkoxy of upto about 12 carbon atoms such as methoxy, ethoxy, propoxy, butoxy,octyloxy, etc.; halogen such as chloro and bromo; alkoxycarbonyl of from2 to about 8 carbon atoms such as methoxycarbonyl, ethoxycarbonyl,butoxycarbonyl, hexyloxycarbonyl, etc.; carboxyl; cyano; alkenyl ofabout 2 to 12 carbon atoms such as vinyl, allyl, etc.; formyl; alkanoylof about 2 to 8 carbon atoms such as acetyl, propionyl, butyryl,hexanoyl, etc.; alkanoylamido of about 2 to 8 carbon atoms such asacetamido, butylamido, etc.; aroylamino such as benzamido; andalkylsulfonamide such as methanesulfonamide, hexanesulfonamido, etc.

Specific examples of the aromatic iodide reactants include iodobenzene1,3- and 1,4-diiodobenzene, 1,3,5-triiodobenzene, 4-iodotoluene,4-iodophenol, 4-iodoanisole, 4-iodoacetophenone, 4,4'-diiodobiphenyl,4-chloroiodobenzene, 3-bromoiodo-benzene, and 2,6- and2,7-diiodonaphthalene. Our process is particularly useful for thepreparation of benzenedicarboxylic and naphthalenedicarboxylic acids andtheir esters and thus the preferred reactants are diiodobenzenes,especially 1,3- and 1,4-diiodobenzene, and diiodonaphthalenes,especially 2,6- and 2,7-diiodonapththalene.

The aromatic iodide reactants are known compounds and/or can be preparedaccording to published procedures. For example, T. Hudlicky et al TheChemistry of Halides, Pseudohalides and Azides, Supplement D, Part 2,1142-1158, the disclosure of which is incorporated herein by referencein its entirety, discloses a number of such processes. Another processdescribed in J. Chem. Soc. 150 (1952) comprises treating an aromaticcompound, such as benzene, with iodine in the presence of silver sulfatedissolved in concentrated sulfuric acid.

The alkanol used in the process of this invention normally is methanolsine it is the least expensive, results in the formation of methylcarboxylate esters, which may be used in transesterification reactions,and produces methyl iodide which is the most volatile of the alkyliodides. However, other alkanols, for example, alkanols containing up toabout 12 carbon atoms, preferably up to about 4 carbon atoms, may beemployed if desired. Examples of such alkanols include ethanol,propanol, butanol, pentanol, hexanol, heptanol, octanol, decanol,ethylene glycol, diethylene glycol, benzyl alcohol, and the like. Ifaromatic esters are desired, about two moles of alkanol are required foreach mole equivalent of iodoaromatic reacting. For each mole equivalentof aromatic acid produced, one mole of alkanol is required.

The process provided by our invention can also be carried out in thepresence of an organic co-solvent such as aliphatic, alicyclic andaromatic hydrocarbons, halogenated hydrocarbons and ethers. Examples ofsuch solvents include benzene, toluene, the xylenes, hexane, heptane,chlorobenzene, ethylene dicholoride, methylchloroform, diethyl ether,methyl t-butyl ether, diglyme, acetic acid, benzoic acid, methylbenzoate, etc. However, the use of a co-solvent is not critical to thepractice of this invention.

The ruthenium catalyst can be provided to the reaction medium as any ofa number of ruthenium salts or complexes that are capable of providingruthenium in a soluble form in the reaction. Illustrative sources ofruthenium are ruthenium trichloride, ruthenium tribromide, rutheniumtriiodide, ruthenium acetate, ruthenium acetylacetonate, rutheniumdioxide, ruthenium tetraoxide, ruthenium pentacarbonyl anddodecacarbonyltriruthenium and their phosphine and halogen substitutedanalogs. The amount of ruthenium is not significant as long as enough ispresent to catalyze the reaction. Preferably, the catalyst is present ina concentration of 10 to 0.01 mole percent, preferably 1.0 to 0.1 molepercent, based on the moles of aromatic iodide reactant. Therefore, thetotal reaction medium has a catalyst concentration of about 10,000 ppmto 10 ppm with preferred catalyst concentrations of 1000 to 100 ppm.

The carbonylation reaction is conducted in the presence of carbonmonoxide, which is employed in amounts such that the total reactionpressure is suitable for the formation of both the aromatic carboxylicester and the alkyl iodide. The carbon monoxide employed may beessentially pure or it may contain other gases such as carbon dioxide,hydrogen, methane and other compounds produced by synthesis gas plants.Normally, th carbon monoxide will be at least 90, preferably at least95, percent pure.

The process of the present invention can be conducted at temperaturesand pressures suitable for formation of both the aromatic carboxylicacid and alkyl iodide. The temperatures and pressures are interdependentand can vary considerably. While the process can be carried out atpressures as high as 10,000 psig, the cost of utilities and equipmentrequired for such high pressure operation cannot normally becommercially justified. Thus, the pressure normally will be in the rangeof about 300 to 4000 psig, preferably about 750 to 1500 psig. Aparticularly preferred pressure is 1000 psig. While temperatures as lowas 125° C. and higher than 225° C. may be used, our process normally iscarried out between about 125° to 225° C. The preferred temperaturerange is 150° to 200° C. A particularly preferred temperature is 175° C.

The relative amounts of carbon monoxide, alkanol and aromatic iodideused in our process can be varied substantially and are, in general, notcritical as long as there is at least a stoichiometric amount present.

When a polyiodo aromatic compound is used as the reactant in ourcarbonylation process, the products obtained include both aromaticpolycarboxylic esters and partially carbonylated products such as iodoaromatic carboxylic esters. The latter compounds are useful asintermediates in the preparation of derivatives of aromatic carboxylicesters, for example, by displacement reactions whereby the iodosubstituent is replaced with other radicals. The difunctional esters,such as dimethyl 2,6-naphthalene dicarboxylate, can be reacted withdiols to produce high molecular weight polyesters suitable for moldingplastics. Useful articles can be molded from these plastics, such as byinjection molding. The relative amounts of partially or totallycarbonylated products is highly dependent on the period of time that thereactant resides under carbonylation conditions. For example, thecarbonylation of diiodobenzene at 175° C. and 750 psig in accordancewith our invention over varying periods of time results in varyingamounts of reactant, iodo ester and diester.

The alkyl iodides prepared according to the process of our invention maybe used in other chemical processes such as in the preparation ofcarboxylic acids and carboxylic anhydrides according to knowncarbonylation procedures. Alternatively, the alkyl iodide can beoxidatively decomposed at elevated temperature to produce a gaseousmixture of iodine, carbon dioxide and water from which the iodine can berecovered. Alternatively, the alkyl iodides may be thermally decomposedto iodine and an alkane.

Our process is carried out at a pKa of less than 5. Therefore, there areno significant amounts of basic materials which preferentially combinewith hydrogen iodide and interfere with the formation of an alkyliodide. Examples of such bases which are not present in significantamounts in our process include amines, particularly tertiary amines, andhydroxides, alkoxides and weak acid salts, e.g. carboxylates, of thealkali and alkaline earth metals.

Our process is particularly useful for the preparation of dialkyl estersof aromatic dicarboxylic acids such as 1,3- and 1,4-benzene-dicarboxylicand 2,6- and 2,7-naphthalene-dicarboxylic acid esters. Such diesters maybe used in the preparation of polyesters such as poly-(ethyleneterephthalate) and poly(ethylene 2,6-naphthalenedicarboxylate).

The process of this invention can be carried out as a batch,semi-continuous or continuous operation. In the manufacture of dialkylesters of aromatic dicarboxylic acids in the quantities required for usein the preparation of polyesters such as those mentioned above, theprocess described hereinabove will be carried out in a continuousmanner. A typical continuous method of practicing our process comprisesfeeding into a mixed pressure vessel a liquid stream of methanol,another liquid stream composed of 2,6-diiodonaphthalene, optionally anorganic solvent and the ruthenium catalyst and a gaseous stream ofcarbon monoxide. The pressure vessel is equipped with a means formaintaining the desired temperature and pressure. The liquid mixturefrom the reactor is passed to a flash column where the methyl iodide andinert organic solvent is flashed off. The flashed vapor stream is thencondensed and the methyl iodide and methanol separated by decanting. Theliquid from the flash column is centrifuged and 2,6-naphthalenedicarboxylic acid is separated from the solution containing the ester of2,6-naphthalene dicarboxylic acid. The desired 2,6-naphthalenedicarboxylic ester is then recovered by selective recrystallization andthe remaining mixture containing unreacted iodoaromatics and rutheniumcatalyst is recycled.

Our invention is further illustrated by the following examples. In theprocedures utilized in the examples the materials employed are loadedinto a 330 ml autoclave constructed of Hastelloy B2 alloy which isdesigned to operate in a rocking mode. The autoclave is pressurized with500 psig carbon monoxide gas pressure at room temperature and then thegas is vented and the autoclave is sealed. In these examples theautoclave is pressurized to 250 psig with carbon monoxide gas at ambienttemperature and heated and rocked until reaction temperature wasreached, at which time additional carbon monoxide gas is added toincrease the autoclave internal pressure to the predetermined value.Reactor pressure is maintained by adding carbon monoxide at the samerate at which it is consumed by the reactants. The carbon monoxide usedis essentially pure. When the predetermined reaction time is completedthe autoclave is cooled by a stream of cold air to approximately 25° C.After the gas is vented from the autoclave the crude product is analyzedby gas chromatographic methods. The % conversion is the mole percent ofiodo-group converted to carboxylic acid or ester. The ester/acid ratiois the mole ratio of total ester and acid groups formed. The grams ofalkyl iodide found were determined by gas chromatographic analysis ofthe reaction solution. The results of these runs are shown below.

    ______________________________________                                        Example No.                                                                   ______________________________________                                                    1            2                                                    Iodoaromatic                                                                              p-diiodobenzene                                                                            p-diiodobenzene                                      wt (g)      20           20                                                   Alkanol     methanol     methanol                                             wt (g)      24           24                                                   Co-Solvent  toluene      toluene                                              wt (g)      56           56                                                   Catalyst    RuCl.sub.3.3H.sub.2 O                                                                      RuCl.sub.3.3H.sub.2 O                                wt (g)      0.50         0.10                                                 Time (Hr)   3            3                                                    Pressure    1000         750                                                  (psig)                                                                        Temp (°C.)                                                                         175          175                                                  % Conversion                                                                              100          45                                                   Ester/Acid  4.3          24.6                                                 g. Alkyl    16           7                                                    Iodide                                                                                    3            4                                                    Iodoaromatic                                                                              iodobenzene  iodobenzene                                          wt (g)      60           61                                                   Alkanol     methanol     methanol                                             wt (g)      39           39                                                   Co-Solvent  toluene      toluene                                              wt (g)      82           82                                                   Catalyst    RuCl.sub.3.3H.sub.2 O                                                                      RuCl.sub.3.3H.sub.2 O                                wt (g)      0.50         0.50                                                 Time (Hr)   4            4                                                    Pressure    1500         4000                                                 (psig)                                                                        Temp (°C.)                                                                         175          175                                                  % Conversion                                                                              39           100                                                  Ester/Acid  7.5          6.5                                                  g. Alkyl    15           40                                                   Iodide                                                                                    5            6                                                    Iodoaromatic                                                                              p-iodophenol 2,6/2,7-diiodonaphtha-                                                        lene                                                 wt (g)      15           25                                                   Alkanol     methanol     methanol                                             wt (g)      39           39                                                   Co-Solvent  toluene      toluene                                              wt (g)      82           82                                                   Catalyst    RuCl.sub.3.3H.sub.2 O                                                                      RuCl.sub.3.3H.sub.2 O                                wt (g)      0.50         0.50                                                 Time (Hr)   4            4                                                    Pressure    1500         1500                                                 (psig)                                                                        Temp (°C.)                                                                         175          175                                                  % Conversion                                                                              100          94                                                   Ester/Acid  10.2         6.6                                                  g. Alkyl    9            16                                                   Iodide                                                                                    7            8                                                    Iodoaromatic                                                                              iodobenzene  iodobenzene                                          wt (g)      60           60                                                   Alkanol     methanol     ethanol                                              wt (g)      40           39                                                   Co-Solvent  acetic acid  toluene                                              wt (g)      99           82                                                   Catalyst    RuCl.sub.3.3H.sub.2 O                                                                      RuCl.sub.3.3H.sub.2 O                                wt (g)      0.50         0.50                                                 Time (Hr)   4            4                                                    Pressure    1500         1500                                                 (psig)                                                                        Temp (°C.)                                                                         175          175                                                  % Conversion                                                                              75           45                                                   Ester/Acid  0.42         5.5                                                  g. Alkyl    30           18                                                   Iodide                                                                        ______________________________________                                    

While the invention has been described in detail with particularreference to preferred embodiments thereof, it will be understood thatvariations and modifications an be effected within the spirit and scopeof the invention.

We claim:
 1. A process comprising:(A) co-production of an aromaticcarboxylic ester and an alkyl iodide by carbonylating an aromatic iodidein the presence of carbon monoxide an alkanol and a catalytic amount ofa ruthenium catalyst under aromatic carboxylic ester and alkyliodide-forming conditions of temperatures and pressure wherein there areno significant amounts of basic materials which preferentially combinewith hydrogen iodide and interfere with the formation of an alkyliodide, and (B) recovering the alkyl iodide.
 2. The process of claim 1wherein the aromatic iodide is selected from the group consisting ofdiiodonaphthalene and diiodobenzene.
 3. The process of claim 2 whereinthe diiodonaphthalene is 2,6-diiodonaphthalene and the diiodobenzene is1,4-diiodobenzene.
 4. The process of claim 1 wherein the alkanol ismethanol.
 5. The process of claim 1 wherein the temperature is in therange of about 125° to 225° C.
 6. The process of claim 5 wherein thetemperature is in the range of about 150°-200° C.
 7. The process ofclaim 1 wherein the pressure is in the range of 300 to 4000 psig.
 8. Theprocess of claim 7 wherein the pressure is in the range of 750 to 1,500psig.
 9. The process of claim 1 wherein the process is carried out inthe presence of an organic co-solvent.
 10. A process comprising(A)co-production of an aromatic dicarboxylate selected from the groupconsisting of a benzenedicarboxylate and a naphthalene dicarboxylate andmethyl iodide by carbonylating a diiodobenzene or a diiodonaphthalene inthe presence of carbon monoxide methanol, an organic solvent and acatalytic amount of a ruthenium catalyst at a temperature of about 150°to 200° C. and a pressure of about 750 to 1,500 psig wherein there areno significant amounts of basic materials which preferentially combinewith hydrogen iodide and interfere with the formation of an alkyliodide, and (B) recovering the methyl iodide.
 11. A processcomprising(A) co-production of dimethyl 2,6-naphthalenedicarboxylate andmethyl iodide by carbonylating 2,6-diiodonaphthalene in the presence ofcarbon monoxide, methanol, an organic co-solvent and a catalytic amountof ruthenium at a temperature of about 175° C. and a pressure of about1,000 psig wherein there are no significant amounts of basic materialswhich preferentially combine with hydrogen iodide and interfere with theformation of an alkyl iodide, and (B) recovering the methyl iodide.